Continued expansion and enhancement of the Mammography Tumor Registry (MTR) in Washington State is proposed in order to build a foundation for collaborative interdisciplinary research on mammography performance in a community setting. New methods for measuring the performance of mammography will be developed which will rely only on the dates of diagnosis and mammograms and characteristics of the tumor, in order to obviate the use of mammographers' coding of the reason for the mammogram, symptoms, assessment, or recommendations for follow up. The methods will be evaluated by analyzing variation in performance among facilities using new and standard methods as well as by using a simulation model to generate a gold standard. Using these measures, the roles of tumor biology, breast density, and hormone use in the failure of mammography will be investigated. The MTR will be expanded by adding 20 facilities selected for their potential contribution to research goals, and enhanced by adding a pathologist, surgeon, medical oncologist/cancer geneticist, and statistician to the investigator team. The database will be enhanced by including measurement of tumor biology (cell proliferation and genetic markers) in selected cases in which characteristics of the patient and mammograms are known. A pilot study is proposed to assess the feasibility of adding electronically transmitted pathology data directly to the MTR to allow timely feedback to mammography facilities to assist them in MQSA compliance. An ancillary study is proposed involving retrospective review of prior films ofrandontly selected cases diagnosed in TNM stage III or IV despite screening in the preceding 2-26 month period.